Catheter incorporating a high column high column strength distal tip region

ABSTRACT

A catheter is disclosed providing a balloon catheter having a distal tip that is flexible while additionally incorporating high column strength. The present invention additionally provides a distal tip region that accommodates for various sized guidewires. In preferred embodiments, the distal tip region is initially configured for accommodating the passage of 0.12-inch guidewires only. Through specific manufacturing processes, however, the distal tip is modified so that it also may be expanded to accommodate the passage of 0.14-inch guidewires. In additional preferred embodiments, an elastomeric sleeve is disposed over the modified distal tip to allow the tip to return to the initial 0.12-inch accommodating profile when the larger 0.14-inch guidewire is withdrawn from the catheter.

TECHNICAL FIELD

The present invention generally relates to the field of intravascularmedical devices used in combination with various sized guidewires. Morespecifically, the present invention relates to intravascular balloondilation catheters using guidewires for crossing occluded stenoticregions, wherein the distal tip region of the balloon dilation catheterincorporates an expandable high column strength distal tip thataccommodates an exchange for a larger diameter guidewire.

BACKGROUND OF THE INVENTION

Intravascular diseases are commonly treated by relatively non-invasivetechniques such as percutaneous transluminal angioplasty (PTA) andpercutaneous transluminal coronary angioplasty (PTCA). These therapeutictechniques are well known in the art and typically involve the use of aballoon catheter with a guidewire, possibly in combination with otherintravascular devices such as stents. A typical balloon catheter has anelongated shaft with a balloon attached proximate the distal end and amanifold attached to the proximal end. In use, the balloon catheter isadvanced over the guidewire such that the balloon is positioned adjacenta restriction in a diseased vessel. The balloon is then inflated and therestriction in the vessel is opened.

There are three basic types of intravascular catheters for use in suchprocedures, including fixed-wire (FW) catheters, over-the-wire (OTW)catheters and single-operator-exchange (SOE) catheters. The generalconstruction and use of FW, OTW and SOE catheters are all well known inthe art. An example of an OTW catheter may be found in commonly assignedU.S. Pat. No. 5,047,045 to Arney et al. An example of an SOE ballooncatheter is disclosed in commonly assigned U.S. Pat. No. 5,156,594 toKeith.

Several characteristics that are important in intravascular cathetersinclude pushability, trackability and crossability. Pushability refersto the ability to transmit force from the proximal end of the catheterto the distal end of the catheter. Trackability refers to the ability tonavigate tortuous vasculature. Crossability refers to the ability tonavigate the balloon catheter across narrow restrictions in thevasculature, such as stenosed vessels or fully and partially deployedstents.

The trackability of a particular catheter design is analyzed in terms ofthe trackability of the distal portion of the catheter. The distalportion is the section of the catheter that must track the guidewirethrough the small tortuous vessels of a patient's vasculature. The sizeof the distal tip, the flexibility of the distal tip, and lumen diameterall influence the trackability of a catheter. Imparting more flexibilityto the distal portion of a catheter, in particular, has been found toimprove trackability. Increasing the flexibility within the distal tipimproves handling and navigation over a guidewire.

To maximize crossability, the present invention is a catheter having adistal tip incorporating high column stiffness. Longitudinal columnstiffness permits the distal portion of a catheter to cross narrowlesions within the vasculature. Flexible distal tips can yield to thepressures required to cross such lesions, thereby rendering the catheterineffective. Further crossability is improved by the physicianwithdrawing the thinner, more flexible guidewire, and replacing it witha thicker and stiffer guidewire. Thicker guidewires add desirablestiffness when crossing tight or totally occluded lesions within thevasculature. Passage across such lesions often requires a greaterlongitudinal stiffness than a thinner guidewires affords. Advancing athicker guidewire over the distal tip achieves this requiredlongitudinal stiffness. Many catheter designs, however, cannotaccommodate the replacement of a thicker guidewire. Often, the thickerguidewire is prevented from advancing through a catheter's distal-mosttip that is designed specifically for thinner guidewires. The smallerdistal tip openings of these catheters allow for easier navigation whenused in combination solely with thinner gauge guidewires.

SUMMARY OF THE INVENTION

The present invention overcomes many of the disadvantages of the priorart by providing a balloon catheter having a distal tip that issufficiently flexible, while additionally incorporating high columnstrength. Additionally, the present invention provides for a balloondilation catheter that is accommodating to both thinner and thickergauge guidewires, depending upon the desired use.

Flexibility in the distal tip region is necessary in order to navigatethe tortuous vasculature within a patient's body. A delicate balance isrequired, however, between making the distal tip adequately flexible fornavigation and making the distal tip adequately stiff for traversingtight lesions. A catheter that can easily reach a desired region deepwithin a patient's body is useless if the catheter cannot cross theregion to treat the diseased area. In effect, the advantages of aflexible and nimble distal tip are diminished if the catheter otherwisebecomes functionless.

The present invention provides a distal tip region of a catheter thatstrikes a balance that negligibly decreases the flexibility of thedistal tip, yet enhances the column stiffness in the same. Using variouscombinations of material, in various arrays and configurations, severalembodiments are disclosed having the desired flexibility and stiffnessrequirements for a distal tip region.

The present invention additionally provides for a distal tip region thataccommodates for various sized guidewires. In preferred embodiments, thedistal tip region is initially configured for accommodating the passageof a 0.012-inch guidewire or a 0.018-inch guidewire. Through specificmanufacturing processes, however, the distal tip is modified so that italso may be expanded during use to accommodate the passage of selectedlarger diameter guidewires such as a 0.014-inch, a 0.018-inch, or a0.035-inch guidewire through the original passage for the 0.012-inchguidewire. Further, in embodiments designed to initially accommodate a0.018-inch guidewire, the distal tip is modified so that it canaccommodate selected larger diameter guidewires such as a 0.035-inchguidewire. In certain embodiments, the distal tip region is expandablefrom about 0.012 inches to about 0.024 inches, preferably to about 0.020inches, although other ranges can be selected such as expanding to about0.038 inches to accommodate a 0.035-inch guidewire or smaller. Inadditional preferred embodiments, an elastomeric sleeve is disposed overthe modified distal tip to allow the tip to return to the initial0.012-inch or 0.018-inch accommodating profile when the larger0.014-inch, 0.018-inch, or 0.035-inch guidewire is withdrawn from thecatheter.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims particularly point out and distinctly claim thesubject matter of this invention. The various objects, advantages andnovel features of this invention will be more fully apparent from areading of the following detailed description in conjunction with theaccompanying drawings in which like reference numerals refer to likeparts, and in which:

FIG. 1 is a partial cross-sectional plan view of a catheter inaccordance with the present invention, having a distal tip regionincorporating a high column strength inner shaft;

FIG. 2A is a partial perspective view of a preferred distal tip regionof the catheter of FIG. 1, illustrating a slit along a portion of theinner shaft forming a tapered distal most tip and a guidewire extendingtherethrough;

FIG. 2B is a partial perspective view of the preferred distal tip regionof FIG. 2A, illustrating the opening of the bond forming the tapereddistal most tip when a larger guidewire is inserted therethrough;

FIG. 3A is a cross-sectional view along 3A—3A of the tapered distal tipof FIG. 2A, showing the positioning of the slit along the inner tubularmember using a smaller diameter guidewire;

FIG. 3B is a cross-sectional view along 3B—3B of the tapered distal tipof FIG. 2B, showing the positioning and relationship of the slit alongthe shaft after exchanging the guidewire in FIG. 3A with a largerdiameter guidewire;

FIG. 4 is a partial perspective view of an alternative distal tip,having a tapered end formed by overlapping a portion of the innertubular member being slit from the distal most end;

FIG. 5 is a partial perspective view of another embodiment of thepresent invention, having a distal tip region incorporating a rigidpolymeric insert having a slit extending along at least a portion of itslength fitted within a portion of the inner tubular member; and

FIG. 6 is a partial perspective view of another embodiment of thepresent invention, having a distal tip region incorporating a helicalcut rigid polymeric insert abutting the distal end of the inner tubularmember.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description should be read with reference to thedrawings, in which like elements in different drawings are numberedidentically. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. Examples of construction, materials, dimensions, andmanufacturing processes are provided for selected elements. All otherelements employ that which is known to those skilled in the field of theinvention. Those skilled in the art will recognize that many of theexamples provided have suitable alternatives that may be utilized.

Referring now to the drawings, FIG. 1 is a cross-sectional view of anover-the-wire (OTW) balloon catheter, which is representative of onetype of catheter that can incorporate the present invention. Otherintravascular catheter embodiments are additionally suitable withoutdeviating from the spirit and scope of the present invention. Forexample, intravascular catheters suitable for incorporating the presentinvention include fixed-wire (FW) catheters and single-operator-exchange(SOE) catheters.

The balloon catheter 10 includes a shaft assembly 12 and a balloonassembly 14 connected proximate the distal end of shaft assembly 12. Aconventional OTW-type manifold assembly 16 is connected to the proximalend of the shaft assembly 12. The shaft assembly 12 includes an innertubular member 18 having a proximal end 20 and a distal end 22. Theproximal end 20 of the shaft assembly 12 extends into a manifoldassembly 16 and is affixed thereto. A polyurethane strain relief 24 issnap-fit to the manifold assembly 16, and the shaft assembly 12 extendsinto the manifold assembly 16 through the polyurethane strain relief 24.An outer tubular member 26 is co-axially disposed about the innertubular member 18 to define an annular inflation lumen therebetween.

Generally, outer tubular member 26 has an outer diameter ranging from0.040 inches to 0.045 inches with a wall thickness ranging from 0.0028inches to 0.0044 inches. Materials used to form outer tubular member 26may vary depending upon the stiffness desired for the shaft assembly 12.Nylon and similar polyamides such as Vestimid or Grilamid areparticularly suitable for rigid outer tubular members. Other suitablematerials for a rigid outer tubular member include polyetheretherketone(PEEK), polyimide (PI), and polyetherimide (PEI). Rigidity mayadditionally be imparted to the outer tubular member 26 by incorporatinga braid on or within the tubular member. Polyether block amide (PEBA),in contrast to the rigid polyamides, is a relatively flexible polymericmaterial having a durometer of approximately 70D. Finally, the use of apolyamide such as CRISTAMID (available from Elf Atochem) imparts aslightly less rigid durometer than the rigid polyamids and slightlygreater than the flexible PEBA material.

The inner tubular member 18 defines a guidewire lumen 28, which providesa passage for a guidewire (not shown). The inner tubular member 18 isgenerally made of polyethylene such as Marlex HDPE. In alternativeembodiments, the inner tubular member 18 is made of a lubriciousmaterial such as polytetrafluoroethylene (PTFE). At the proximal end ofthe inner tubular member 18, the inner tubular member 18 has an outsidediameter ranging from 0.022 inches to 0.030 inches, and most preferablyabout 0.025 inches. In one preferred embodiment, the inner diameter ofthe inner tubular member 18 measures approximately 0.018 inches to 0.023inches, allowing for a 0.014-inch or 0.018-inch guidewire. The innertubular member 18 has a wall thickness ranging from 0.0026 inches to0.004 inches, and most preferably about 0.0032 inches for a 0.014-inchor 0.018-inch lumen. Alternative lumen diameters can be selected foraccommodating other guidewire sizes. The outside diameter-to-wallthickness ratio must be sufficiently small to minimize the propensityfor the shaft assembly 12, and more specifically the inner tubularmember 18, from kinking.

Balloon assembly 14 includes a balloon body portion 30 with a proximalballoon waist 32 and a distal balloon waist 34. The proximal balloonwaist 32 is connected to the outer tubular member 26 near its distal end40 by means of an adhesive, or alternatively, by thermal bonding. Thedistal balloon waist 34 is connected to the inner tubular member 18 nearits distal end 22 by means of an adhesive bond or a thermal bond suchthat the interior of the balloon 33 is in fluid communication with theannular inflation lumen.

FIGS. 2-6 show embodiments incorporating various designs within thedistal tip region 50 of the catheter 10 of FIG. 1. In general,flexibility in the distal tip region 50 increases tracking performancewithin the tortuous vasculature of a patient. The distal tip region 50needs to yield to navigate over a previously advanced guidewire. Incontrast, it is also desirable to have a distal tip region 50 that hashigh column strength in order to cross occluded and tight lesions withina vasculature. In addition, catheters 10 more easily track and navigateover narrow guidewires than thicker guidewires. The distal tip region 50of a catheter 10 can more easily yield and turn with a thinner guidewirethat is also yielding. Thicker guidewires possess increased stiffness.Increased stiffness prohibits an advancing catheter 10 from easilynavigating the twists and turns of a human vasculature. Thus, it isdesirable to manufacture a distal tip region 50 that is flexible fortracking through the vasculature, yet includes enhanced column strengthfor crossing tight lesions. It is additionally desirable to manufacturea catheter 10 that contains a distal tip opening suited for thinnerguidewires, yet is expandable to accommodate thicker guidewires incertain circumstances. FIGS. 2-6 disclose embodiments of the presentinvention being convertible from a first outer diameter to a secondouter diameter, and having a longitudinally stiff, while tangentiallyflexible, distal tip region 50.

FIGS. 2A and 2B depict two configurations of a preferred distal tipregion 50. The length of the inner tubular member 18 at the catheter'sdistal tip region 50 is exaggerated or shown without the distal balloonwaist for illustrative purposes only. Often, the distal balloon waist 34is positioned just proximal the distal-most end 62 of the catheter 10.In particular, FIG. 2A illustrates a distal end 22 of an inner tubularmember 18 having a gradually tapered distal tip 60. FIG. 2B illustratesthe same inner tubular member 18 as shown in FIG. 2A, however, thetapered distal tip 60 of the inner tubular member 18 has been expandedto accommodate a larger guidewire.

FIG. 2A specifically shows a preferred distal tip region 50 of thecatheter 10 of FIG. 1, having a gradually tapered distal tip 60.Emerging from the tapered distal tip 60 is a guidewire 70 having asmaller outer diameter, such as 0.012 inches. The guidewire 70 is shownin phantom. The tolerance between the inner diameter of the distal-mostend 62 of the tapered distal tip 60 and the outer diameter of theguidewire 70 is minimal. The tolerance between the inner diameter of theinner tubular member 18 and the guidewire 70 proximal the distaltapering is significant when compared with that at the distal-most end62 of the tapered distal tip 60.

In a preferred embodiment, the tapering of the distal tip region 50 ofFIG. 2A is formed by cutting and removing at least one section of innertubular member 18, as best illustrated in FIG. 2B. The enlarged distaltip 61 of FIG. 2B further illustrates the cutting configurationnecessary to achieve the tapered distal tip 60 of FIG. 2A. A segment ofinner tubular member 18 is removed having a wedge shape. The base of thewedge is the distal-most end 62 of the inner tubular member 18. Thesides of the wedge taper inwardly as the sides move proximally from thedistal-most end 62. The apex 64 of the wedge, therefore, is at a pointproximal the distal-most end 62 of the inner tubular member 18. Multiplewedge sections covering less area may alternatively be removed aroundthe diameter of the inner tubular member 18 to achieve the desiredtapered configuration. Hereinafter, an inner tubular member 18 having awedge of material removed from the distal most-end 62, as described indetail above, will be referred to as a “modified inner tubular member66.”

In one embodiment, a tapered distal tip 60 is formed from the modifiedinner tubular member 66 using a mandrel (not shown). The distal end ofthe mandrel preferably includes a tapered end. The modified innertubular member 66 is loaded over the mandrel until the modified innertubular member 66 is aligned with the mandrel's tapered end. Themodified inner tubular member 66 is then held against the mandrel'stapered end forming a tapered distal tip 60. The tapered distal tip 60includes at least one bonded section 68 having a single line of fissurewhere the walls of the modified inner tubular member 66 are positionedtogether. A shrink-wrap material is generally then placed over thetapered distal tip 60 in order to secure the modified inner tubularmember 66 within the tapered configuration. The walls of the modifiedinner tubular member 66 are then adhesively or thermally bonded togetherin order to maintain the tapered configuration. The shrink-wrap is thenremoved, if originally applied, forming the final tapered distal tip 60.

The formed tapered distal tip 60 of FIG. 2A, however, may be made tofissure under the correct circumstances, discussed in detail below. Inparticular, the insertion of a guidewire 72 having a diameter greaterthan the smaller or 0.012-inch wire may be used to break the bondedsection 68 of modified inner tubular member 66.

Materials may be added to the inner tubular member 18 to increase columnstiffness without decreasing flexibility within the distal tip region50. In one embodiment, the section of inner tubular member 18 formingthe tapered distal tip 60 may be longitudinally striped with variousblends of polymeric materials. In particular, the inner tubular member18 may include several longitudinally extruded materials varying inrelative stiffness. Alternating a stiff polymeric material next to aflexible polymeric material provides enhanced column support withoutsignificantly decreasing flexibility within the striped area.

In another embodiment, the alternating polymeric materials may beextruded in a spiral configuration. A twisting polymeric extrusionhaving different durometers resists compression and, therefore,increases column strength without significantly decreasing flexibilityin the distal tip region 50.

In yet another embodiment, additional reinforcing filamentous materialsmay be added to the distal tip region 50 of the catheter 10. Stainlesssteel, nitinol and polymeric filaments can be added to the extrudedinner tubular member 18 to increase column stiffness withoutsignificantly decreasing flexibility.

FIG. 2B is a partial perspective view of the preferred distal tip region50 of FIG. 2A, having a larger diameter guidewire, such as a 0.014- or0.018-inch guidewire 72, inserted therein. As described above, the innertubular member 18 includes a diameter that permits a larger guidewire 72(shown in phantom) to be slidably disposed therein. A larger guidewire72, however, may not traverse the opening distal-most end 62 of thetapered distal tip 60 shown in FIG. 2A. The distal-most end 62 of thetapered distal tip 60 in FIG. 2A generally only permits a smallerguidewire, such as a 0.012-inch guidewire 70, to slidably passtherethrough. The advancing larger guidewire 72 possesses an outerdiameter greater than the size of this opening at the distal most end62.

When the advancing larger guidewire 72 contacts the tapered section ofthe tapered distal tip 60, the force applied by the guidewire 72 spreadsapart the bonded section 68 forming the distal taper. Initial opening ofthe bonded section 68 along its line of fissure generally occurs at thedistal-most end 62 of the tapered distal tip 60. The bond 68 then opensfrom this location proximally until the larger guidewire 72 may passtherethrough. The bond 68, therefore, may not necessarily be entirelyfissured or broken.

After a portion of the bond 68 forming the distal taper is broken, theouter diameter of the modified inner tubular member 66 forming thetapered distal tip 60 is generally equivalent to the outer diameters ofthe other sections of inner tubular member 18 throughout the shaftassembly 12. As described above, however, the bond 68 need notnecessarily open entirely to permit the passage of the larger guidewire72. The enlarged tapered distal tip 61 may still impart a slight tapercaused by the unbroken portions of the bond 68. Whether opened entirelyor not, the larger guidewire 72 is now capable of being easily advancedpast the opening at the distal-most end 62 of the enlarged distal tip61.

Once the bond 68 forming the tapered distal tip 60 is opened, theopening at the distal-most end 62 generally remains in the openedconfiguration. In an alternative embodiment, however, an elastomericsleeve (not shown) may be placed over the bonded segment 68 forming thetapered distal tip 60 shown in FIG. 2A. The elastomeric sleeve imparts aconstricting pressure on the surrounding modified inner tubular member66, forcing the tapered distal tip 60 to return to a taperedconfiguration if the larger wire is removed. When a larger guidewire 72opens the bonded segment 68 enlarging the tapered distal tip section 61,the elastomeric sleeve permits an enlargement only necessary for theguidewire 72 to be slidably displaced therethrough. Once the largerguidewire 72 is removed, the elastomeric sleeve constricts the enlargeddistal tip section 61 into its original tapered configuration 60. Thisembodiment is particularly useful for re-crossing stents and stenoticregions where an enlarged distal tip section 61 may cause thedistal-most end 62 of the catheter 10 to be “hung-up” on the stent orsurrounding tissue.

FIGS. 3A and 3B are cross-sections of the embodiments of FIGS. 2A and 2Balong the lines 3A—3A and 3B—3B, respectively. Lines 3A—3A and 3B—3Btraverse the distal tip region 50 of their respective views. Thecross-sectional view of FIG. 3A shows the narrow tolerance between thesmaller guidewire 70 and the walls of the inner tubular member 18. Thiscross-sectional view further shows the disruption of continuity in thewall of the inner tubular member 18. In particular, the bonded line offissure 68 is shown where the wall of the inner tubular member was cutto form the tapered distal tip configuration 60 of FIG. 2A.

FIG. 3B additionally shows the disruption of the continuity in the wallof the inner tubular member. The larger guidewire 72 is shown havingopened the bonded line of fissure 68 forming the tapered distal tipconfiguration 60 of FIG. 2A. The cross-sectional view particularly showsthe large gap 74 in the wall of the inner tubular member 18. The gap 74is sufficiently large enough to enlarge the distal tip 61, but narrowenough not to permit the guidewire 72 from escaping the lumen that innertubular member 18 defines.

The use of multiple wedges (not shown) forming the modified innertubular member 66 can further confine the guidewire 72 within the innertubular member 18. Multiple wedges individually remove less tubularmaterial, thereby limiting the size of any single gap 74 in the wall ofthe inner tubular member 18. Reducing the size of a gap 74 additionallyreduces the possibility that the guidewire 72 may extend through thatgap 74.

Refer now to FIG. 4, wherein an alternative embodiment for the distaltip region 50 of the catheter 10 of FIG. 1 is shown. The tapered distaltip 63 is formed by making a lateral cut 76 into the larger innerdiameter inner tubular member 18. The lateral cut 76 extends from thedistal-most end 62 of the inner tubular member 18 proximally to a pointdistal from the waist of the balloon 34. Unlike the embodiment depictedin FIG. 2A, however, a wedge-shaped section is not removed from theinner tubular member 18 in FIG. 4.

Forming the distal tip region 50 in FIG. 4 can be accomplished by theuse of a mandrel (not shown). The mandrel is advanced through the innertubular member 18 until the distal tip of the mandrel emerges from thedistal-most end 62 of the catheter 10. In preferred embodiments, thedistal tip of the mandrel includes a slight tapering. The portions ofinner tubular member 18 adjacent the lateral cut 76 are then overlapped,seen in phantom, to conform to the tapering of the mandrel. Theoverlapped portions of inner tubular member 18 are then shrink-wrappedand processed using thermal techniques to impart a tapered distal tip63. The shrink-wrap is then removed from the tapered distal tip 63 andthe mandrel is withdrawn from the catheter 10. The processed tapereddistal tip 63 of FIG. 4 includes an opening at the distal-most end 62having an inner diameter such as 0.012 inches or greater to accommodatea smaller guidewire. The inner diameter proximal the opening at thedistal-most end 62 gradually tapers from the smaller diameter to alarger diameter, such as an inner diameter that accommodates a0.014-inch, 0.018-inch, or 0.035-inch guidewire 72. It is also notedthat FIG. 4 discloses inner tubular member 18 including two portionsjoined under the balloon waist 34 by a butt joint 19, with the distalportion 21 forming the tip 63.

In operation, a physician advances the catheter 10 in FIG. 4 over asmaller diameter guidewire 70. When the physician comes across aparticularly difficult occlusion to cross, the physician withdraws thesmaller guidewire 70 and advances a larger guidewire 72 through thepositioned catheter 10. Tubular support is imparted to the catheter 10as the larger diameter guidewire 72 approaches the distal-most end 62 ofthe catheter 10. After reaching the tapered distal tip 63 of thecatheter 10, the physician applies a greater advancing pressure upon theguidewire 72 to fissure the processed tapered distal tip 63. When theprocessed tapered distal tip 63 is fissured, the lateral cut 76 opens toits original or larger inner diameter. The larger guidewire 72 is thenfully advanced through opening at the distal-most end 62. With the addeddistal tubular support, the catheter 10 may cross tight or totallyoccluded lesions within the vasculature.

Expanding the processed tapered distal tip 63 may be a non-reversibleoccurrence. After expansion, the enlarged distal tip can remain with thelarger inner diameter configuration for the remainder of the operation.In one embodiment, however, an elastomeric sleeve (not shown) may besecured over the tapered distal tip 63 in FIG. 4. The elastomeric sleeveimparts a constricting force upon the diameter of the inner tubularmember 18. When the tapered distal tip 63 is expanded, the elastomericsleeve counteracts the increased diameter profile of the tapered distaltip 63. In certain embodiments, once the larger guidewire 72 iswithdrawn and replaced with a smaller guidewire 70, the elastomericsleeve reduces the profile of the enlarged distal tip to its originallyprocessed configuration.

FIG. 5 shows another embodiment of the present invention having a distaltip region 50 incorporating a rigid polymeric insert 82. Columnstiffness within the distal tip region 50 permits the catheter 10 tomore easily cross difficult lesions and occlusions. It is generallyundesirable, however, to have an entire distal tip region 50 comprisingstiff polymeric material. Navigation through a patient's tortuousvasculature increases in difficulty with increased distal tip stiffness.Therefore, unlike the previously described embodiments, the embodimentin FIG. 5 incorporates a rigid insert 82 whose structure may be variedto increase column stiffness within specific desired regions of acatheter's distal tip 80. Only specific areas within the distal tip 80are desired to be made rigid for heightened column support. Theremaining portions of the distal tip 80 will remain quite flexible forenhanced navigation and trackability within a patient's vasculature. Arigid insert 82 allows for such selectability. The materials, shapes andsizes of the rigid insert 82 may all be modified to accommodate specificvascular applications.

Rigid insert 82 is generally made of stiff polymeric materials.Materials suitable for the rigid polymeric insert 82 include nylon andsimilar polyamides such as Grilamid or Vestamid, as well as other rigidpolymers such as polyetheretherketone (PEEK), polyimide (PI), andpolyetherimide (PEI). In alternative embodiments, the stiffness withinthe rigid insert 82 is modified by altering the composition within therigid insert 82. For example, materials may be added to the rigid insert82 to increase column stiffness while enhancing flexibility. In oneembodiment, the rigid insert 82 may be longitudinally striped withvarious blends of polymeric materials. In particular, the rigid insert82 may include several longitudinally extruded materials varying inrelative stiffness. Alternating a stiff polymeric material next to aflexible polymeric material provides enhanced column support withoutsignificantly decreasing flexibility within the striped area of therigid insert 82.

In another embodiment, the alternating polymeric materials forming therigid insert 82 may be extruded in a spiral configuration. A twistingpolymeric extrusion having varying durometers resists compression and,therefore, increases column strength. This increase in column strengthoccurs without significantly decreasing flexibility of the rigid insert82, as well as the entire distal tip region 50 as a whole.

In yet another embodiment, additional reinforcing filamentous materialsmay be added to the rigid insert 82. Stainless steel, nitinol andpolymeric filaments can be added to a less stiff polymeric material toform a rigid insert 82. This embodiment forms a rigid insert 82imparting increased column stiffness without significantly decreasingflexibility.

The rigid insert 82 is generally pre-shaped to mimic the profile of alumen within a catheter 10. Specifically, the rigid insert 82 is shapedto conform to the lumens within the distal tip region 50 of the catheter10. In one embodiment, specifically illustrated in FIG. 5, the distalend of the rigid insert 82 is positioned at the distal-most end 62 ofthe distal tip 80. The rigid insert 82 extends proximally from thedistal-most end 62 of the catheter 10 to a point proximal the distal endof the balloon waist 34. The size of the rigid insert 82 may be reducedsignificantly to increase flexibility within the distal tip region 50for navigation and trackability purposes. The lengths and sizes of therigid insert 82, therefore, may be easily varied without deviating fromthe spirit and scope of the invention. For example, in an alternativeembodiment, a supple polymeric material (not shown) is positioned distalthe rigid insert 82. This configuration permits the supple polymericmaterial to act as an atraumatic distal tip. The formation of anatraumatic distal tip, in combination with a rigid insert 82, fails toaffect the column stiffness caused by the introduction of the rigidinsert 82 within the distal tip region 50 of the catheter 10.

The initial inner diameter of the rigid insert 82 generally accommodatesthe passage of a smaller guidewire, such as a 0.012-inch guidewire 70.In a preferred embodiment, the rigid insert 82 abuts the inner tubularmember 18, forming a continuous, uninterrupted inner lumen that extendsto the distal-most end 62 of the catheter 10. In an alternativeembodiment, the rigid insert 82 is fitted over the inner tubular member18. In yet another embodiment, the rigid insert 82 is fitted within thelumen formed by the inner tubular member 18.

FIG. 5 specifically shows a butt joint formed between the rigid insert82 and the inner tubular member 18, wherein the rigid insert 82 abutsthe end of inner tubular member 18. If the rigid insert 82 is fittedeither over or under the inner tubular member 18, a lap joint must beformed. The lap joint seals the portion of overlap between the twostructural elements. Sealing the two structural elements togetherensures fluid continuity and structural integrity within the distal tipregion 50 of the catheter 10. When lap joints are formed, a polymericbackfill may be added to the lap joint to smooth the transition betweenthe various structural elements. Backfilling the lap joint, inparticular, permits an advancing guidewire 70 or 72 to cross easily overthe joint without resistance. An advancing catheter 10 generallyexperiences resistance when the lap joint is particularly disjointed. Inthe present case, disjointedness occurs most frequently when a thickwalled rigid insert 82 is fitted within the inner tubular member 18.Backfilling is needed less when the rigid insert 82 is fitted over theinner tubular member 18.

Although the rigid polymeric insert 82 is generally stiff, the insert 82may expand radially. Expansion of the rigid insert 82 is often aided byvarious manufacturing techniques. In a preferred embodiment, alongitudinal slit 84 is imparted along the length of the rigid insert82. In alternative embodiments, multiple longitudinal slits 84 areimparted along the length of the rigid insert 82. The rigid insert 82,as described above, may comprise any selected material. In general,however, all the materials suitable for the rigid insert 82 permit adegree of compliance to conform to a newly expanded configuration.

Expansion of the distal tip 80 occurs when a guidewire 72 of a greaterdiameter, such as a 0.014-inch, a 0.018-inch, or a 0.035-inch guidewire,is advanced through the inner tubular member 18. As the larger guidewire72 enters the region including the rigid insert 82, the rigid insert 82radially expands to accommodate the larger guidewire 72. The distancebetween longitudinal slits 84 opens until the guidewire 72 may cross theentire length of the insert 82. The guidewire 72 is then furtheradvanced until the guidewire 72 exits the catheter 10. When the largerguidewire 72 is withdrawn from the catheter 10, the rigid insert 82 mayor may not reduce its diameter profile to its original configuration. Inparticular embodiments, an elastomeric sleeve 86 is disposed over thelength of rigid insert 82 to reduce the outer diameter of the insert 82after guidewire 72 withdrawal. Controlling the radial expansion of therigid insert 82 is of particular importance when re-crossing stents andstenotic regions where an expanded distal tip 80 may cause the distalend of the catheter to be “hung-up” on the stent or surrounding tissue.

Material selection for the elastomeric sleeve 86 includes thosematerials having desirable expansion and compliance characteristics. Theelastomeric sleeve 86 needs to be capable of expanding to a radialdiameter, and furthermore, retracting back to the generally same initialdiameter. Materials suitable for the elastomeric sleeve 86 includegenerally flexible thermoplastic materials. In preferred embodiments,the elastomeric sleeve 86 is comprised of polyamide, polyetherelastomer, ethylene vinyl acetate (EVA), polyurethane, or latex, as wellas other suitable thermoplastic elastomers. Specific polymers caninclude PEBAX, Tecothane or Grilamid.

In embodiments having the rigid insert 82 inserted under the innertubular member 18, the stiffness of the inner tubular member 18 mayreduce the outer diameter of the rigid insert 82 back to into originalconfiguration. In alternative embodiments, as well as the one previouslymentioned, the elastomeric sleeve 86 controls the uniform rate ofexpansion and contraction of the rigid insert 82. In many instances, thematerials forming the elastomeric sleeve 86 and the inner tubular member18 generally fail to bond with the materials forming the rigid insert82. In order to obtain proper adhesion between the dissimilar materials,other mechanical means must be utilized for bonding purposes. In apreferred embodiment, a mechanical lock 92 is formed between theelastomeric sleeve 86 or inner tubular member 18 and the rigid insert82.

During manufacturing, a plurality of holes 88 is milled through thewalls of the rigid insert 82. The plurality of holes 88 generallyextends along the entire length and circumference of the rigid insert82. The size of holes 88 milled generally depends upon the desiredapplication of the catheter 10, and the materials used in forming theelastomeric sleeve 86 or inner tubular member 18. The modified rigidinsert 82 is then inserted over a mandrel. The outer diameter of themandrel forms a tight friction fit with the inner diameter of themodified rigid insert 82. The polymeric material used to form theelastomeric sleeve 86 or inner tubular member 18 overlays the modifiedrigid insert 82 and mandrel. The polymer, when heated, flows into eachof the holes 88 previously milled into the rigid insert 82. When theelastomeric polymer hardens, the mandrel is removed.

The inserted sectional view 90 of FIG. 5 best illustrates the resultingmechanical lock between the two dissimilar materials. Section 90 showsthe phantom removal of a portion of rigid insert 82. “Fingers” 92 ofpolymeric material are shown extending down from the body of the innertubular member 18 into the spaces where holes 88 would be located thoughthe rigid insert 82. These fingers 92 fill the annular space of theholes 88 preventing the longitudinal displacement between the rigidinsert 82 and the inner tubular member 18. Furthermore, the fingers 92often anchor the inner tubular member 18 to the rigid insert 82, therebyalso preventing the vertical displacement between the rigid insert 82and inner tubular member 18.

Refer now to FIG. 6, wherein an alternative embodiment for the distaltip region 50 of the catheter 10 of FIG. 1 is shown. The distal tipregion 50 is formed similarly to those embodiments utilizing a rigidpolymeric insert 82 as described in reference to FIG. 5. As such, theplacement, length, materials of the insert 94 of FIG. 6 are similar tothose described above, however, unlike the previous embodiments, thepresent embodiment incorporates a helical cut into the rigid insert 94.

In one preferred embodiment, as depicted in FIG. 6, the helically cutrigid insert 94 proximal portion is fitted under the distal balloonwaist 34 and abuts the distal end of the inner tubular member 18 so thata lap joint 96 is formed at the rigid insert's most proximal end by thedistal waist 34. This is preferably the only attachment site for thehelically cut rigid insert 94. Anchoring the proximal portion of thehelically cut rigid insert 94 with the distal portion extending beyondthe distal balloon waist 34 allows those portions of the rigid insert tomove freely. The helically cut rigid insert 94 may bend in any directionby displacing the “windings” 98 forming the helically cut rigid insert94. The helically cut rigid insert 94 is depicted in an expanded state,allowing passage of a larger wire. In a preferred embodiment, the distalportion would be formed with a tapered portion which expands as thelarger wire passes therethrough. Alternatively, the helically cut rigidinsert 94 can be fit within the inner tubular member 18, with thisdesign additionally reducing the opening at the distal-most end 62 ofthe distal tip region 50 to an inner diameter that accommodates thepassage of a smaller guidewire 70, such as a 0.012-inch wire.

Expansion of the distal tip region 50 incorporating a helically cutrigid insert 94 occurs when a guidewire 72 of a larger diameter, such as0.014 inches or 0.018 inches, is advanced through the inner tubularmember 18. As the larger guidewire 72 enters the region including thehelically cut rigid insert 94, the windings 98 of the rigid insert 94displace. More specifically, the windings 98 slide along one another,expanding at least a portion of the helically cut rigid insert 94 from afirst diameter to a second diameter. When the larger guidewire 72 iswithdrawn from the catheter 10, the helically cut rigid insert 94similarly reduces its diameter profile to its original configuration byunwinding the helically cut rigid insert 94.

In particular embodiments, an elastomeric sleeve 86 is disposed over thelength of helically cut rigid insert 94 to reduce the outer diameter ofthe insert 94 after guidewire 72 withdrawal. Controlling the radialexpansion of the helically cut rigid insert 94 is of particularimportance when re-crossing stents and stenotic regions where anexpanded distal tip section 50 may cause the distal end of the catheter10 to be “hung-up” on the stent or surrounding tissue.

Material selection for the elastomeric sleeve 86 includes thosematerials having desirable expansion and compliance characteristics. Theelastomeric sleeve 86 needs be capable of expanding to a radial diameterand, furthermore, retracting back to the generally same initialdiameter. Materials suitable for the elastomeric sleeve 86 includegenerally flexible thermoplastic materials. In preferred embodiments,the elastomeric sleeve 86 is comprised of polyamide, polyetherelastomer, ethylene vinyl acetate (EVA), polyurethane, or latex, as wellas other suitable thermoplastic elastomers. Specific polymers caninclude PEBAX, Tecothane or Grilamid.

Numerous characteristics and advantages of the invention covered by thisdocument have been set forth in the foregoing description. It will beunderstood, however, that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size and ordering of steps without exceeding the scope of theinvention. The invention's scope is of course defined in the language inwhich the appended claims are expressed.

What is claimed is:
 1. A balloon catheter assembly comprising: an outertubular member having a proximal end and a distal end; an inner tubularmember coaxially disposed within at least a portion of the outer tubularmember having a proximal portion and a distal portion with a lumenextending therethrough, the proximal portion of the inner tubular memberhaving a first column stiffness and a first flexibility, the distalportion of the inner tubular member having a second column stiffnesssimilar to the first column stiffness and a second flexibility greaterthan the first flexibility, the distal portion of the inner tubularmember having a longitudinal cut with ends abutting to form a taperedtip being expandable from a first outer diameter to a second outerdiameter wherein the first diameter is smaller than the second diameter;and an inflatable balloon having a proximal end affixed proximate thedistal end of the outer tubular member, and a distal end affixedproximate the distal portion of the expandable tubular member.
 2. Theballoon catheter assembly of claim 1, wherein the distal portion of theinner tubular member includes at least one longitudinally extending slitthrough a wall thereof along at least a portion of the length of thedistal portion of the inner tubular member.
 3. The balloon catheterassembly of claim 1, wherein the at least one longitudinally extendingslit extends along at least a portion of the length of the inner tubularmember.
 4. The balloon catheter assembly of claim 1, wherein at leastpart of the distal portion of the inner tubular member tapers distally.5. The balloon catheter assembly of claim 1, wherein the distal portionof the inner tubular member expands from an inner diameter of about0.012 inches to an inner diameter of about 0.024 inches.